CometWatch checks up on Cheops

This four-image NAVCAM montage comprises images taken on 8 October from a distance of 16.9 km from the centre of comet 67P/C-G, so roughly 15 km from the surface.

Comet 67P/C-G on 8 October, from a distance of 16.9 km from the centre of the comet. Credits: ESA/Rosetta/NAVCAM

The view covers the bottom and side of the larger lobe of the comet, and highlights the large, smooth region that is home to a number of large boulders, including ‘Cheops’, as seen in yesterday’s close-up view from OSIRIS.

The NAVCAM image scale at this distance is about 1.25 metres/pixel, so each 1024 x 1024 pixel frame is nearly 1.3 km square (the four full-resolution individual images making up the montage are provided at the end of this post). The montage has been rotated 90 degrees clockwise to place the region containing Cheops at the top for emphasis; the four individual frames are in the original orientation.

When seen in this side-on view, Cheops appears much more like its Egyptian pyramid namesake and has a height of approximately 25 metres, compared with a width of 45 metres as seen from above in yesterday’s OSIRIS image. For reference, the real Pyramid of Cheops at Giza is 139 metres high and 230 metres across at the base.

Be sure to let your eye trace around the profile of the comet, too, and take in some great new views of dramatic cliffs and ‘spires’.

OSIRIS has a wide range of filters in both its NAC and WAC channels, and so can make colour images. However, with a comet that is in reality very dark and very grey, making meaningful colour images is actually quite difficult, in terms of calibration, accurate image registration, and colour balancing.

The OSIRIS team have been working hard on this, I understand, but don’t have something they’re happy to release yet.

In this spec at page 39 there is a nice colour composition of the Orion nebula made with the Osiris NAC.
On page 20 the filters and their purposes are described to some extent. Making artistic eye catching pictures is not the main goal. If a picture from Osiris is published, most likely it is a broad band red colour filter inserted, correct me if I’m wrong.

Yes. But how about release “raw-jpeg” images, exactly like JPL is doing with MER, MSL, MRO, Cassini, etc. ? And leave them in the hand of amateur image-workers ?
I really appreciate the outreach effort conduct by the ESA with NAVCAM datas, but why keeping OSIRIS data away from the public space ?

There is no real colour to see. Since 67P/C-G consists of different shades of black, some dark grey and infrequent lighter (but still dark) grey. So there’s no red sand like on Mars or anything like that.

Also cameras on Rosetta might not have colour sensors, but instead use filters in front of the sensor to record separate red/blue/green images which are then combined to produce a colour image. The movement of the spacecraft and the rotation of the comet might make colour images difficult to achieve because the different images would not register properly. You can see already the difficulty in getting quick successive shots of different parts of the comet in the images above.

Actually there is. Osiris is an extremely advanced camera that captures images in a large range of wavelengths. Visible light falls between 400 to 700nm EM. Osiris instruments capture i believe between 200 and almost 1000nm EM. So that is the full visible and even beyond the visible spectrum.

But don`t forget these are Navcam images not the Osiris images. Those will apparently (most of them) not be released for some time so that ESA scientists can develop new discovery papers before others, after all it’s a European taxpayers funded mission and all the work was done by these scientists).

Lets also not forget the comet is darker than charcoal. So most images are best seen adapted to this degree. As they said previously they would have to share almost fully black images if they wanted to show what the comet really looked like.

The NAVCAM (which is an italian-built instrument) has no colour filters. OSIRIS AWC and NAC cameras have several filters and will produce “colour” images for scientific purposes, not necessary similar to what the human eye would see.

Why do I get the impression that the debri and shape of the Comet seems to stream back from the right hand side of the picture?
Is this possibly the original impact face of the Comet? If so then the boulders may well be scattered from those impacts and would explain the random positions in the dust fields.
There is so much about this Comet that needs rational explanation and not conjecture as this is,’ A never seen before’ situation.
We basically do not know where it has been or what has happened to it in its travels around the Universe for Eons.
Perhaps at some time it has been impacted and this started it spinning slowly and we now see the results of this.

There will be no real “colour images” because 67P is basically the same colour as a barbeque charcoal briquette or supermarket car park – black. Black, with hints of black here and there, and patches of black inbetween, It’s even blacker than the monitor screen at ESA maked “Latest image from OSIRIS”. ..

Every time we get a different viewpoint there are crazier things to see. Rocks appearing to sit on flat planes at impossible angles, ledges and cliffs that confound you as to how they haven’t collapsed, let alone how they got that way. Cheops does “APPEAR” to be on a slope it could have slid down. What this image does show is the nature of the squiggly line we saw on the image from OSIRIS taken way back on 3/8/2014. And again in the close up taken of the area on arrival day. (see yesterdays blog.)

It appears to be a small cliff that traces something like a fault line where either some displacement along the fault has taken place or “erosion” has dug depressions into the surface. The depressions and ridges we se are non-circular, so seem unlikely to be related to impact craters. The hight of the little scarp is not consistent and at points disappears to just a furrow with little circular depressions along it, just as can be seen in the neck area.

These lines of vents/hollows/depressions/furrows appear in many places associated with brighter areas beside them. Further away from Cheops along the “fault line” there are thick “rays” of less dark material. Ejecta or lighting effects?

“Every time we get a different viewpoint there are crazier things to see. Rocks appearing to sit on flat planes at impossible angles, ledges and cliffs that confound you as to how they haven’t collapsed, let alone how they got that way.”

Robin S., this poses a question I’ve been itching to ask ever since we first saw the “dumbbell” shape of the comet weeks ago (even though I’m not a professional mathematician or physicist): exactly WHERE is the centre of gravity of such an irregular, twin-lobed object? Is it somewhere in the “body” or, (less likely, given its apparently smaller size), somewhere in the ”head”? Or maybe even in “mid air” somewhere between the two lobes of the comet, in the henceforth celebrated “neck” region? Or does each lobe possess its own centre of gravity, proportional to its mass?

Me too. The comet rotates about its centre of gravity so from the animations and the Longitude /Latitude grid produced by ESA, it is in the neck area sightly nearer the body end. I tend to think of it as a two body system, because of the small amount of mass in the neck area. Each lobe has, then its own centre of gravity separate from the system’s centre, like the Earth and the Moon.

The gravity on the surface of each lobe would be dominated by this, but on the areas facing each other across the neck is where I get really confused. Given the larger mass of the body, would not the surface under the head lobe, the massive cliff we see, have a negative surface gravity? Yet we still see some ejecta deposits on the ledges of that cliff. Then there are centripetal forces to consider.

As a working orientation guide, I just take the gravity vector of each area on the surface of the lobes, as being towards the centre of the lobe you are looking at. Even that is confusing, as across just one of the NAVCAM images, that gravity vector might change by 90+ degrees. Along the neck the gravity is just very low and just off perpendicular to the surface at an angle towards the body lobe. This means over the small area of the neck it changes significantly over only tens of metres.

Its certainly very alien to one’s intuition and makes making sense of what we see extremely problematic, especially on a 2D image.

@Robin S. Thanks for this very thoughtful analysis, which I fully agree with.

I’l also intrigued by the implications of these gravitational complications for calculating the density of the comet. We’re told that the figure we’ve been given of roughly 40% of that of water has been calculated on the basis of the gravitational attraction the comet exerts on the Rosetta probe. This attraction has necessarily been taken into account in determining the burn-times required to put Rosetta on its different orbits. But as we have discussed, the twin-lobed nature of the comet must make the necessary calculations considerably more complicated than we are led to believe. My guess is that there has been need for much brilliant improvisation and that the actual mass of the comet as a whole, and hence its density, is still far from being firmly established.

I also surmise that one of the reasons for finally choosing the “J” site for the Philae landing may have just as much, if not more, to do with these gravitational complications as with the intrinsic scientific interest of the “J” site terrain itself. The gravitational attraction exerted on Philae as it falls towards the comet will be much easier to calculate and is likely to remain much more stable during the descent if Philae is released, as now planned, from directly “above” the head lobe. It will thus benefit from the undivided attraction of the total mass of the comet as a whole. An attempted landing anywhere nearer the neck region would presumably be made more complicated in terms of precision by having to take into account the vying gravitational attractions of the two main lobes during Philae’s descent, as we have been discussing.

I think you’ve hit the nail on the head there about the landing site options. The back up site C is on the outer half of the big lobe and once again, although not quite so straightforward, the gravity vectors should be less of a guess.

Now Rosetta is in its 10Km orbit, resolution of the gravity field variations should be easier. The gravitational effects on Rosetta’s orbit being larger, smaller scale variations will be easier to pick out from the noise. The doppler shifts in the radio signal they are using to make these gravity determinations, must be tiny.

Image 4, about half way up on the lefthand side is a feature shaped like a “7”. The top of the “7” appears to be almost flat and relatively bright. Zooming in on this ledge there seem to be 3 pits in the dust/regolith with white circles at the bottom, one of them has two white circles. This can admittedly only just be made out, but its well before pixelation becomes a factor.

To the right of this ledge is what looks like a landslide of scree and rubble. It stops half way down the sheer cliff. Follow it up to its source and zoom out. It looks like thick lumpy treacle running down the cliff. It doesn’t spread out into a fan like one might expect. How does that work?

Re. “Color”
Remember that the surface dust is the “color” of the black toner in a laser printer. On Earth, it would look like a huge lump of black coal, except coal is shinier (more specular). These images have enhanced brightness and contrast so that surface features are clearly visible. If there are areas with higher albedo, it would be interesting to know their actual colors relative to the actual reflectance of the rest of the surface, rather than just showing the “enhanced” versions.

The visual “color” of the comet is not relevant. It is black. The purpose of the filters in the science cameras is to provide images over a wide range of wavelengths. By analyzing the values numerically or evaluating the visual “spectral signature”, the mineralogical or chemical makeup of the surface materials can be determined.

Even evaluating the albedo (“brightness”) of the surface materials under differing phase angles (“lighting conditions”) can tell us a lot about the physical characteristics.

Big thank you Emily (and ESA) for almost daily new set of images from NAVCAM!
Those are the best images from NAVCAM to date!
Not only because of high resolution but it’s really nice and dramatic shot of “the body”.

It is mind bugling to try to imagine why the dust sees are see like at all. In this low gravity anything solid and dust or sand like could impossibly float around and flatten due to low viscosity. If draped due to regathered material then it should be more uniform all over the place. There is nothing in my mind that can explain this circumstance. There are even waves on this sees as seen in the Osiris closeup. I suppose the persons at ESA that are analyzing the gathered data are quite busy and as scientist with ambitions and an urge to stay in good reputation will be very conservative and not in any way speculative, in sum we will have to wait for quite a long time until anything substantial is on display. Remember how long it took until we got the Osiris close up and how little of data there actually is to be extracted out of this image. Essentially its artistic property is the only satisfaction to gain.

Well… it might be challenging to reproject the different channels into a common viewpoint to assemble a color image but by no means impossible. You would need a very exact shape-model but with the massive volume of data from OSIRIS that should not be so hard to produce.

Then you have to create color from the B/W color filtered images. that is a bit tricky because OSIRIS does not have an ordinary cameras R G and B color filters. You would have to use multiple images shot trough different filters to estimate the spectrum in each pixel. Then you convert the spectrum to CIE color and from there to sRGB for monitor display.

Several times 3D images have been mentioned and in some images this has been done,
To take 3D images the 2 pictures really should be taken simultaneously but this is not possible with one camera on Rosetta.
There is also the objects shift due to rotation and Rosettas path moving against the object.
A solution might be to mount 2 cameras at the extremities of 2 arms of a known base length eg. 2 mtrs. and then pictures cam be captured for 3D use.
Much valuable information can be obtained from 3D pictures as the visual perception is more lifelike.
Perhaps in future missions this idea can be used for research.
Clive

Hi Logan, the principle of 3D is that the image can have fiducial markings on them which help measure distance on the image. Also the relative size of objects like Cheops.
There is something very satisfying viewing an image in 3D because it gives the ability to look around an object.
No doubt such an image recording may have been considered, but as needs must alternate methods are employed to save bandwidth and weight. But still desirable.

Curiosity was supposed to have a 3D camera but it was dropped from the project. It is suggested it might be on the next Mars Rover. I also agree 3D would be useful, though i can understand that it doubles the bandwidth needed and that may be another reason why it is not used. Also, extra weight, more things to break, etc.

After looking closely at the OSIRIS image of “Cheops”, I tried to find a picture to give an idea of what the flat plain around it might look like. The original was a colour image so I have desaturated it and tried to darken it so that it appears more like 67P as seen in other ESA images. I think the bumps might be a little bigger and steeper because of the low gravity. I am not saying it does look like this, its just the impression I got.

It will be interesting to see how it compares to colour images the OSIRIS team say they are working on. I presume this coloration was done using similar techniques to how they turn old B&W films into colour. As I understand it there needs to be some initial colour “reference” to extrapolate the others. In this case it must be a guess, making the whole colour spectrum a guess. Regardless of its scientific accuracy its still an amazing image.

Hi Logan. I was confused by this until I realised that this area is on the “top” of the body lobe. Gravity is acting almost 180 degrees differently from the area where Cheops is located. If you rotate image 4 counterclockwise by 90 degrees, the edge of the plains are actually sloping upwards to cliff edges, which then cast the shadow seen to the right. Further along the edge of the plain, there are rows of “rocks” sitting at the bottom of the slopes.

The feature I thought was “like lumpy treacle” is not running down a cliff face it is a ledge at the bottom of a cliff, and the adjacent plain at the bottom of a very large, deep pit. I am indebted to Mattias and his 3D animation for clarifying this for me. Definitely required viewing. Just superb. Zooming in and traversing the 3D anaglyph is spectacular.

This ‘tongues of hanging material’ have their shadows ‘very pointy’ too. This is not the behavior of a ‘chocolate’ or ‘tar’ material. Would like to know if there is iron minerals in this ‘flowing prairies’.

I think you might be right there Logan. Rubble generated from the “prairies” appears to be angular and block like, where other rubble from other sources is more rounded. Is this a function of time exposed to “erosion”, or a sign of the different makeup of the areas?

I’m thinking the latter. If these parries are from cryovolcanic frozen “lava” flows, they would have a great deal of crystalline structure. Other areas of “original” comet would, according to the accretion idea, be made up of random and round shaped “rubble”. The only flaw is, where did the internal energy for such volcanism come from?

Indeed. These look more like how I would expect impact craters to look, with a central mound in the middle of raised circular walls. I had not spotted any that obvious before.

That broken plate just “above” the Cheops plain you spotted is looking very much like a layer of material that has flowed over the underlying layers. The lower layers appear to have eroded more quickly from underneath and the overhang broken off. The interesting thing is the very linear/cubic composition of the material and the fact it has maintained its structural integrity. The conclusion is it is less volatile and less porous, just as molten comet material that had frozen would be. While molten, the more volatile components would boil out and pores collapse, leaving a more crystalline, compact and stronger layer.

Thats what it looks like anyway, other interpretations and ideas no doubt could apply. I for one am more and more convinced there was at some time in the past “molten” comet material flowing on the surface. How else can we explain so many large areas of even, flat surface on an object that is basically rugged, rough and uneven.

Images 3 and 4 are essentially looking at the rim of the body lobe. The whole lobe seems to have been squashed and flattened by the gravity of the head lobe. Such is the brittle nature of the material, this seems to have fractured the surface severely, revealing the interior structure of the comet. In the left half of image 4, this is very clear, revealing a conglomerate or aggregate material. Large “boulders” and “rocks” in a matrix, presumably of melted ices, that looks very similar to Roman concrete. In the completed mosaic there is a definite line of very rugged, rubbly, gouged, terrain running all around the edge of the lobe.

Due to the greater mass of the body lobe, the effect on the head lobe seems to have had even more severe consequences. The fracturing seems to have split the bottom part of the head lobe completely off, creating the shear cliff we see on the underside of the head. The huge crater at landing site A could be where a very large lump fell from the head lobe.

Possible evidence for this can been in this image taken from above the head lobe looking towards the body lobe showing some of the surface of the “top” of the body. At about 2 O’Clock on the edge of the head, there is a large chunk missing, as if someone has taken a bite out of it. Immediately “below” on the body lobe is a huge crater containing landing site A.

Further evidence of impacts on the body lobe can be seen in this image. The end of the body lobe looks to have been knocked off by some “giant flint knapper”. Chunks falling from the head might have done this.

“The huge crater at landing site A could be where a very large lump fell from the head lobe” . This possible connection between “missing” part and “large crater” could, I suppose, also be due to hard a impact by a small object, in turn ripping off a piece and then releasing the rest of its energy a little further on? I imagine a “piece” even this large would simply deposit as a pile of rubble and not leave a crater.

I like your scenario Jacob. The reason Site A was not chosen was because, in order to land there, Philae would have to be dropped from above the head and take just such a trajectory, within 30m of the edge of the head. Too risky! This was explained in a NASA lecture yesterday by one of the NASA engineers working with ESA on navigation. ESA just said it was impossible to land there.

It certainly is one of the deepest craters we have seen, along with the smaller, even deeper one just next to it. Both would have taken a large, high energy object to create them. That is if they are actually impact craters. I’m not so sure any more, such large impacts would have serious consequences for the integrity of such a brittle and porous object. My new pet theory is Cryovulcanism.

Hi Logan. The further the comet material is away from the equator of the lobe, the more structured and layered it appears to be. The big formations on top of the “head” also exhibit a more evident solidity and structure. Why and what this means, I have no idea.

Not sure I can fully understand your reasoning, but there are other methods to consider.
Where bites have been taken, some are undoubtedly from the collapse of the thin wall. Also the term looks like a bite taken out, may be just that ie a bite. If electrical discharge is considered, it is easy to see how such a hole in a rim occurrs.
Also do you think all these craters are from collisions?, some are odd shapes, they are generally perpendicular to a surface and criss cross each other in many odd ways not consitsant with collision.
The huge craters rely on the belief that something slowly nudged up to the comet with out destroying the comet and with out giving up enough energy to some how weld to the comet.
Further some of the craters look hexogon like with out all being squashed up like in a bee hive where a hexigon is a nateral effect of stacking.

Hi Dave. Too right. There are any number of possible scenarios. I quite like Jacob’s, the chunk of the head knocked off by incoming fire, before hitting the lower lobe. This is probably a more reasonable explanation for the fracture face on the big lobe. I just like to consider slightly less obvious possibilities. Take some basic physics and generate a plausible scenario. Doesn’t mean its correct, likely or even possible, but one of them might be. Objections, arguments against, alternative solutions or even agreement may tease out some answers or help someone else see what is actually going on. I’ve no reputation or academic position to maintain.

My reasoning was, fractures and faults created by the squashing of the head would lead to the weakening and shattering of the lower area of, what might originally been a more spherical object. Being gravitationally attracted to the larger mass, body lobe, the loosely held chunks could be pulled from underneath the head. At some point the gravity of the material at the top of the head will exert enough force to prevent this happening and a line of zero gravitational potential would be formed. This would potentially form a fairly fat surface, the observed shear faces under the head. The long line of “boulders” on the neck plain seem to line up along another line of zero gravitational potential between the large and small lobes. There would be a ring around the neck perpendicular to the centre of gravity of the comet, a sort of “Lagrange Circle”. Perhaps these are the last remnants of what fell off the underside of the head lobe.

Personally I am starting to think that the majority of the “Flat” circular/hexagonal features are more like partially eroded calderas created by Cryovulcanism. The mechanism for such large eruptions is a mystery, especially as they appear to have taken place a very long time ago, before 67P moved into its current orbit closer to the Sun. Maybe at some time in the past it orbited Jupiter and underwent tidal heating like Io.

This Cryovulcanism would have removed large amounts of volatiles and dust from the interior of the comet. The comet could be full of empty chambers. It certainly could explain the low density. Hopefully CONSERT will reveal if that is the case. It could also explain why the comet appears to be way more dusty than expected.

Two NASA members of the Rosetta team gave a 1 hour lecture on the Rosetta mission yesterday. I was hoping they might be a bit less coy about revealing some of 67Ps secrets. No such luck. That the comet was dustier than expected was the only new piece of information that could be gleaned. Their shape model was nowhere as big as ESA’s at the landing announcement, but it was black and more shiny. A 3D printed version of the 3D model released by ESA a few days ago obviously, the lack of texture detail on the back and bottom was a bit of a give away.

My only consolation from the lecture is that the scientist appeared to be as non plussed by what Rosetta has found, as the rest of us. The theories and explanations I suspect, will be a long time coming.

My experience of academic degree scientists is that they protect their projects like alligator mothers protect their eggs. They can keep on doing this as long as they can convince their management that this is needed. Also the management has an urge to keep on going for as long as possible due to obvious reason.

In the private industry it is the opposite behaviour and if engineers are not cooperating to solve their problems and be productive they leave their job positions in flat trajectories. Of Course the secrets stay inside the company but only to leave the competition behind.

I see no reason to compete with this kind of product and the Rosetta Project is owned by the Taxpayers, it is only managed by ESA because our politicians got convinced that this amount of money was for a good purpose.

Personally i do agree that it is its money worth but i do not agree at all to the way the information outside the walls are blocked of in a way that is to be described as paranoid.
We already know that the old models are molded and smelly.

I suppose this is true for every blog, but let me stick to those like this one which have technical information, that it attracts audiences of different degrees of sophistication. For example, I am a working scientist with an amateur interest in planetary and space science, that too way below that of an active amateur and blogger like Stuart Atkinson.

I am curious about comets, but all the discussion about various cometary theories goes above my head. All I can figure from looking around here and there is that majority opinion is in the process of moving from dirty snowballs to icy dirtballs, and to seeing what the ices are made of and what the dirt is made of. (I said this in a talk to schoolchildren last year.) Some of the discussion on 67P is whether even the latter is an adequate model. It is not clear to me what the punchlines of the “alternative” models are.

On a different but related note, does someone in ESA public relations have the time and the inclination to do some social data analysis regarding whom their blogs attract?

Hi Kamal. It is interesting to see the various comet models that the mission is based on. Cometastalker gave a link to the technical spec for OSIRIS. On page 6,7 & 8 there is an outline of comet formation theories and what needs to be observed to clarify the processes going on at the nucleus. This document is not shy in telling us that nothing is known about comet nuclei other than it does contain a large amount of volatile ices, the infamous “dirty snowball”. How the ingredients of ices, dust and rock are distributed and in what ratios is what Rosetta has been sent to find out.

The implication that this will define how all comets formed and are constructed, is another one of those “sound bites”, specifically designed to garner public and political support. Comparisons with data from other comets visited can illuminate the bigger picture, it is claimed. The qualitative and qualitative differences in those data sets from the Rosetta data, makes me doubt that assertion too.

For myself, I just want to know about this comet, theories and inferences about the “big questions” at this stage are impossible. What are the likely mechanisms for the things we have all seen on the few fascinating pictures released so far? Guessing and speculating is part of the initial phase, surely 10 weeks in we have enough information to move on to using hard data to eliminate most possibilities and narrow down the probabilities in the same way the landing site was chosen. What do the experts think is going on? Not what they can prove in scientific papers and journals, but to give us the public some of the basic understanding so far gained. I am sure that the science briefings on landing day will attempt to do this, I just think it should be done sooner to maintain the public interest and support.

ESA thinks another “selfie” will do that apparently. As an interested observer, with or without a science background, that is not enough and it should not be enough for ESA’s political masters either.

It only takes one catastrophic collision, to create a shower of fragments, upset orbital motions and start a chain reaction of further collisions and fragmentation. The dreaded “Gravity” scenario in low Earth orbit. It seems totally improbable that 67P has not been hit by numerous small, fast moving, projectiles during its lifetime. What is perplexing is there is so little visual evidence of this. We see plenty of evidence of this on other small solar system bodies like moons and asteroids. Rapid erosion or surface renewal can be the only explanations for this.

I think the rings of saturn is a nice miniature model of our solar system creation. The guardian moons representing some planets. The difference is that Saturn never “ignited” and its “solar wind” could not sweep the dust away. Our sun did ignite and cleaned out the trash to be mixed with that part of the great cloud that was no part oft the creation process. Comets are nothing but poluted leftovers.

“The huge crater at landing site A could be where a very large lump fell from the head lobe” . This possible connection between “missing” part and “large crater” could, I suppose, also be due to hard a impact by a small object, in turn ripping off a piece and then releasing the rest of its energy a little further on? I imagine a “piece” even this large would simply deposit as a pile of rubble and not leave a crater.

Calculating with the comets head mass to be 0.25E13 kg and the body to be 0.75E13 kg and the rotation period to be 12.4 hours the comet is too long if uniform or has slowed down its rotation speed or is not uniform or a bit from all of it. It would be nice to know if the comet actually is uniform in density as this can be measured by the close orbit the rosetta is performing. Is this a secret or can you share?

Apologies if this information can be found elsewhere (and please point me in the right direction) but can someone tell me whether there is any current consensus on whether 67P is a contact binary that merged from 2 original sources, or the ‘neck’ is the result of ablation of a single, original body? Thanks.

several persons in the public have an idea of how this comet was created and this recipe can be found in several blogs. Quite a few persons at ESA have ideas about the same question but none of them is confident enough to make this public.
I guess in five years when 90% of the outcome of this mission is published we still don’t know how comets are created we only think we know how this one was created.

To save time you can make a guess and be just about as correct in your assumption as the rest of us on both sides of the river.

There is a clue in our solar system of what might be going on outside of our field of view and that is the ring system around Saturn and other planets plus the Asteroid belt.

Nobody knows what this i about even if it sits on our noses, so how can we ever tell what goes on in the black beyond by just observing a handful of samples of those species presented to us by a no chance at all provability.

There are some for free apps available to play around with orbiting bodies i space and if you try some of those you might get an insight of how complex orbits can get in two dimensions newtonian calculations. Morphable orbital or so. Some more professional apps are also available but not for free and if you think this is your way then at first take a look at the rings of saturn and realise that no SW within the next few decades wil be able to copy such a complex dance of bits and pieces.

If you use one of these apps and setup two bodies orbiting each other the shape of the comet in concern. Then add a trace of particles orbiting this binary you soon find out why rosetta is orbiting the 67P/C-G in counter direction of the comets rotation and not in the same direction, there is a major difference in orbital stability of those two scenarios.

Does the water in the coma come from the rock or hidden water ice below the surface?
In this extract from a NASA paper, they show that it could be either or even both.

They even went as far as to erarradiate some silcates in the lab, to show that a sustntial 10% of the emissions to be hydrogen or hydroxils. This means that even with no ice on the surface the the tail would contain the elements suggesting water water, just from the the solar wind tearing apart the surface rock. Of course there is no data yet that confirms silcates on the surface, maybe the dust though.

As no ice has yet been seen, it has to be a possibility, doesnt it?

Here is an interesting NASA article in which it is conceded that the presence of the hydroxyl radical in the coma does not necessarily imply the existence of water on comets. 14.6. INFERENCES ON THE NATURE OF COMETS FROM EMISSION CHARACTERISTICS

The assumption of ices as important bonding materials in cometary nuclei rests in almost all cases on indirect evidence, specifically the observation of atomic hydrogen (Lyman [Greek letter] alpha emission) and hydroxyl radical in a vast cloud surrounding the comet, in some cases accompanied by observation of H20+ or neutral water molecules. In addition, CH3CN, HCN, and corresponding radicals and ions are common constituents of the cometary gas envelope. These observations can be rationalized by assuming (Delsemme, 1972; Mendis, 1973) that the cometary nuclei consist of loose agglomerates containing, in addition to silicates (observed by infrared spectrometry (Maas et al., 1970)) and also water ice with inclusions of volatile carbon and nitrogen compounds.

It has been suggested by Lal (1972b) that the Lyman a emission could be caused by solar wind hydrogen, thermalized on the particles in the dust cloud surrounding the comet. Experiments by Arrhenius and Andersen (1973) irradiating calcium aluminosilicate (anorthite) surfaces with protons in the 10-keV range resulted in a substantial (~10 percent) yield of hydroxyl ion and also hydroxyl ion complexes such as CaOH.

Observations on the lunar surface (Hapke et al., 1970; Epstein and Taylor, 1970, 1972) also demonstrate that such proton-assisted abstraction of oxygen (preferentially O16) from silicates is an active process in space, resulting in a flux of OH and related species. In cometary particle streams, new silicate surfaces would relatively frequently be exposed by fracture and fusion at grain collision. The production of hydroxyl radicals and ions would in this case not be rate-limited by surface saturation to the same extent as on the Moon(for lunar soil turnover rate, see Arrhenius et al. (1972)).

These observations, although not negating the possible occurrence of water ice in cometary nuclei, point also to refractory sources of the actually observed hydrogen and hydroxyl. Solar protons as well as the products of their reaction with silicate oxygen would interact with any solid carbon and nitrogen compounds characteristic of carbonaceous chondrites to yield volatile carbon and nitrogen radicals such as observed in comets. Phenomena such as “flares,” “breakups,” “high-velocity jets,” and nongravitational [236] acceleration are all phenomena that fit well into a theory ascribing them to the evaporation of frozen volatiles. However, with different semantic labels the underlying observations would also seem to be interpretable as manifestations of the focusing and dispersion processes in the cometary region of the meteor stream, accompanied by solar wind interaction.

The MIRO instrument, a mini radio telescope, on Rosetta has 8 different frequency bands to detect the specific emissions of a number of molecules. Three of them are for Water molecules, each one for water containing a different Isotope of Oxygen. Other specific molecules are Carbon Monoxide, Ammonia and two versions of Methanol. This is not detecting hydroxyl ions, but complete Water molecules. It is this instrument which gave us the two Water emission rates of 300ml/s and 5000ml/s.

Well that sounds like a plausible idea to me and fit one of the four speculated comet (snowball) compositions.

The neck area could have been excavated by a very large volcanic explosion initially I suppose. Without the thermal insulation of the very dark, porous and dusty surface layer, erosion by sublimation of the comet’s inner ices rapidly increased and the resulting increased tidal stresses increasing that activity further.

I still lean towards the contact binary scenario, but exactly why the neck area should be preferentially eroded in that scenario I am not sure. The heat generated by such a fusion would surely have compacted and strengthened the material in this region, driven off many of the more volatile compounds and raised the melting/sublimation point of the whole region.

A nice example Logan. This means the aggregate of small planetesimals held together by a matrix, cement if you like, of porous volatile ices, would offer such little resistance to small high velocity impacters, they would bury themselves inside the body of the comet. The space behind them as they travel through the comet along with the energy transferred by friction, would allow the sides of the tunnel to melt and sublimate. The huge expansion of the resulting gases would create a “magma tube” below the surface with enough energy to produce volcanism on the surface. This volcano would then remove any trace of the original impact site.

I like this idea a lot. The period of heaviest bombardment would have been early in the comets life and so the processes of erosion would have had time to reduce the volcano cones to circular features and the central “lava” plugs left behind by some would be slowest to erode, hence the solid crystalline mounds we see. Because of the comet’s rotation the tops of the lobes would be exposed to the most incoming fire, explaining why we see an increased amount of such features on the top of the lobes.

The large crater on the bottom of the big lobe containing Cheops could well have added to the squashed look of the lobe as well and the stratification we see from the shock wave. The shock waves internal reflections may have been enough to chip off the ends of the lobe creating the clean flat edges at either end of the big lobe.

The head lobe also has a large crater, landing site B, on its top and a similar edge with a clean flat break. It too is also squashed, though not so much.

Much is made of the dual flashes seen on comet Temple 1when it was impacted. The first would be as the projectile impacted the relatively solid but thin subsurface layer, the second flash the resulting volcanic eruption of cleaner ice from inside the comet. The crater was seen to have been largely filled in afterwards, presumably by the erupting “lava” that did not leave the surface after the initial release of all the high pressure gases. Comeatstalkers little experiment showed that the resulting refrozen ice would be very porous with a low density, but it would still retain most of the structural integrity of the comet by being confined within the “magma tube”.

No doubt further evidence will appear to make all that total baloney, but I’m going with that for now.